You have here a (good) graphic explanation (PDF, 56Kb). In fact it is quite simple: digitalize content and upload it so it can be accessible to much more places than by using usual broadcasting means.

Nothing new under the sun? Maybe. But content was not there and now it is. And better: digitalized content is so specifically thought for educational purposes and so specifically thought for the target it wants to reach that I don’t doubt it is having a very deep impact (as facts and figures seem to show).